Self-standing container

ABSTRACT

A petaloid base ( 14 ) for a self-standing container ( 10 ) is described. The base ( 14 ) has a central longitudinal axis ( 12 ), a spheroidal underlying base contour, and a plurality of spheroidal foot formations ( 16 ) that interrupt and project from the underlying base contour to define a corresponding plurality of feet ( 16 ). Each foot formation ( 16 ) has an elliptical intersection with the underlying base contour, the elliptical intersection defining a transition between the underlying base contour and a foot formation ( 16 ). A ratio of D 2 :D 1  is in the range of 1:1 to 1:1.38, wherein D 1  is a radial distance from the central longitudinal axis ( 12 ) to a junction between the base ( 14 ) and a side wall ( 48 ) of the self-standing container ( 10 ), and D 2  is a radial distance from the central longitudinal axis ( 12 ) to a radially outermost extremity of the transition.

This invention relates to self-standing containers, more specifically to an integrally moulded petaloid base for such a container. Such containers may be blow-moulded of plastics material such as polyethylene terephthalate (PET).

As will be understood in the art, the generic term ‘PET’ includes compositions that predominantly contain polyethylene terephthalate—but may also including other materials. For example, a suitable composition may comprise approximately 95% polyethylene terephthalate and 5% nylon. As is known in the art, these materials may be mixed, or provided in different layers, for example via multilayer injection moulding and over-moulding.

Blow-moulded PET containers have long been used as bottles for beverages. More recently, they have been proposed for use as kegs for transporting, storing and dispensing beverages such as beer. An example of such a keg is disclosed in WO 2007/064277. The broad concept of WO 2007/064277 is not limited to any particular use, material or method of manufacture of a container. However, the invention has particular advantages in the context of thin-walled blow-moulded containers of the type apt to be manufactured from PET. It is in that context that the invention will be described in this specification.

Early PET containers had a plain hemispherical base and were rendered self-standing by the attachment of a separate base moulding to the base (i.e., a base cup). Whilst a hemispherical base is simple, light and strong in isolation, the addition of a separate base moulding increases material and production costs and may hinder recycling.

In order to make a PET container self-standing without recourse to a separate base moulding, it is now well known to provide the container with an integrally-moulded petaloid base. The term ‘petaloid’ refers to a multi-footed base shape whose feet are disposed in an angularly-spaced arrangement around the base, the resulting shape resembling the petals of a flower when viewed from under the container in use. The container usually has a cylindrical side wall of circular horizontal cross-section, in which case the feet typically lie on a contact circle that is concentric with, and whose diameter is smaller than, the circular cross-section of the side wall. The feet act together to provide a stable multi-point support for the container.

There is continual pressure in the art of containers to reduce material and production costs and to ease recycling. Not only has this led to the adoption of one-piece containers with petaloid bases, but efforts continue to improve the petaloid base so that containers can be produced more economically, while still performing reliably during storage, transportation and use. It is particularly desirable to reduce the amount of material necessary to give the container sufficient integrity and stability for commercial use. Even a small saving of material per container has a massive effect on the cost of production when reproduced across potentially tens to thousands of millions of containers per annum.

The correct trade-off between the amount of material used and the integrity of the container is especially important when the container is to be used as a pressurised vessel. For example, the container may be used for storing, transporting and dispensing effervescent beverages, such as beer. The beverage itself may be carbonated, or a propellant gas may be injected into the container at super atmospheric pressure to force the beverage out of the container. Such a container needs to withstand these internal pressures under a range of environmental conditions. As well as withstanding internal pressures, the container needs to be able to survive rough handling during transportation of the container.

A recent example of a self-standing container that addresses the above considerations is described by the Applicant in United Kingdom Patent No. GB 2479451. The contents of specifications associated with this patent are hereby incorporated by reference to the extent allowed by applicable law.

GB2479451 describes a petaloid base for a self-standing container, the base having a spheroidal underlying base contour and a plurality of spheroidal foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet.

Each foot formation has an elliptical intersection that extends smoothly into the underlying base contour. The foot formations radiate from a central protrusion, the central protrusion extending to a level beyond a lowermost apex of the underlying base contour and having a radius of curvature smaller than a radius of curvature of the underlying base contour. Each foot formation is joined to the central protrusion via a smoothly curving transition portion whose curvature is converse to the curvature of the foot formation and the central protrusion, such that the foot formation, the smoothly curving transition portion and the central protrusion together define a sinuous cross section. An undulating wall section is defined by inner portions of the foot formations, by valleys between the foot formations, and by the central protrusion.

These features in combination provide benefits such as maximising the strength and capacity of the container, while minimising material usage. However, there is still a need for further improvements in the field of self-standing containers. Improvements such as lower material usage, lower production cost, improved standing stability and improved performance under pressure and elevated temperature are constantly being sought.

It is against this background that the present invention has been devised.

According to a first aspect of the present invention there is provided a petaloid base for a self-standing container, the base having a central longitudinal axis, a spheroidal underlying base contour, and a plurality of spheroidal foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet. Ideally, each foot formation has an elliptical intersection with the underlying base contour, the elliptical intersection defining a transition between the underlying base contour and a foot formation. Preferably, the ratio of:

-   -   D₂:D₁         is in the range of 1:1 to 1:1.38; wherein:     -   D₁ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the underlying base contour,         corresponding to a junction between the base and a side wall of         the self-standing container; and     -   D₂ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the transition.

More preferably, the ratio of D₂:D₁ is between 1:1 and 1:1.2. Most preferably, the ratio of D₂:D₁ is 1:1.056±3%.

Ideally, a ratio between any two of: D₁, D₂, D₃, D₄, D₅, D₆, D₇, D₈, D₉, D₁₀, D₁₁, R_(A), R_(B), R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) can be derived by expressing the corresponding values in the following Table A as ratios of one another:

TABLE A D₁ 32.75 D₂ 31 D₃ 6 D₄ 25 D₅ 12.5 D₆ 18.6 D₇ 20 D₈ 28 D₉ 27.6 D₁₀ 13.5 D₁₁ 7.7 R_(A) 6.3 R_(B) 4.2 R_(C) 21 R_(D) 3.6 R_(E) 189 R_(F) 9 R_(G) 8.9 R_(H) 11.7 R_(I) 24.8

Thus, for example, the ratio of D₅:D₄ is 1:2, the ratio of D₃:D₇ is 3:10 and so forth. Preferably, the value of each parameter D₁, D₂, D₃, D₄, D₅, D₆, D₇, D₈, D₉, D₁₀, D₁₁, R_(A), R_(B), R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) should be considered to be within a tolerance of ±5%, more preferably within a tolerance of ±2%.

In the above Table A, and hereinafter:

-   -   D₁ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the underlying base contour,         corresponding to a junction between the base and a side wall of         the self-standing container;     -   D₂ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the transition;     -   D₃ is the radial distance between the central longitudinal axis         and a radially inner end of a foot formation;     -   D₄ is the radial distance between the radially inner end of a         foot formation, and radially outermost extremity of the         transition;     -   D₅ is the widest distance between two points on a foot formation         which are radially equidistant from the central longitudinal         axis and which do not form part of the transition;     -   D₆ is the widest distance between two points on the transition         which are radially equidistant from the central longitudinal         axis;     -   D₇ is the radial distance between the central longitudinal axis         and a contact point of a foot formation;     -   D₈ is the axial distance between a planar surface on which a         foot formation rests when standing and the radially outermost,         axially uppermost extremity of the underlying base contour,         corresponding to a junction between the base and a side wall of         the self-standing container;     -   D₉ is the axial distance between a planar surface on which a         foot formation rests when standing and the radially outermost,         axially uppermost extremity of the transition;     -   D₁₀ is the axial distance between a planar surface on which a         foot formation rests when standing and a line, parallel to that         planar surface that passes through the two points on the         transition which are the furthest apart from one another, and         which are also radially equidistant from the central         longitudinal axis;     -   D₁₁ is the axial distance between a planar surface on which a         foot formation rests when standing and a line, parallel to that         planar surface that passes through the two points on the foot         formation which are the furthest apart from one another, and         also radially equidistant from the central longitudinal axis,         but do not form part of the transition;     -   R_(A) is the radius of curvature of a foot formation within a         section plane intersecting a contact point of the foot         formation, the section plane being parallel to and radially         spaced from the central longitudinal axis. Ideally, R₁ is the         radius of curvature at the contact point;     -   R_(B) is the radius of curvature of the transition within a         section plane intersecting a contact point of the foot         formation, the section plane being parallel to and radially         spaced from the central longitudinal axis;     -   R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) are radii of         curvature measured within a section plane parallel with and         intersecting both the central longitudinal axis and a contact         point of the foot formation with:         -   R_(C) being the radius of curvature of the underlying base             contour between a radially outermost extremity of the             underlying base contour and a radially outermost extremity             of the transition;         -   R_(D) being the radius of curvature of the transition             between the base contour and a radially outermost extremity             of the foot formation;         -   R_(E), R_(F), R_(G) being the radii of curvature of the foot             formation taken at approximately equi-spaced intervals             between the radially outermost extremity of the foot             formation and the contact point, with R_(E) being the radius             of curvature closer to the radially outermost extremity of             the foot formation, R_(G) being the radius of curvature             closer to the contact point, and R_(F) being the radius of             curvature of the foot formation between R_(E) and R_(G),         -   R_(H) being the radius of curvature of the foot formation at             the contact point; and         -   R_(I) being the radius of curvature of the foot formation             radially between the contact point and the central             longitudinal axis.

It should be noted at all the above-referenced radial distances are measured along a plane to which the central longitudinal axis is perpendicular. Similarly, axial distances are measured along an axis perpendicular to that plane.

The Applicant has empirically determined that the relationship between these features, (in particular, the relative proportions as denoted by the above ratios) allows the petaloid base of the first aspect of the invention to retain advantages such as improved strength and capacity associated with the container described in United Kingdom Patent No. GB 2479451—but with lower material usage than this prior known base. The base of the first aspect also benefit from other advantages as will be discussed below.

For example, the ratio between D₁ and D₇ relates to standing ability of the base; the more closely matched the ratios are, the better the standing ability of the base. This derives from the contact points of the foot formations being distributed over a larger surface area relative to the average cross sectional area of the container supported by the base.

Other ratios, or combination of ratios, relate to further advantages. For example, certain ratios are associated with the size of the transition relative to the base contour, and so also the smoothness of that transition with the base contour. A smoother transition reduces unfavourable material distribution in the base, and so reduces the chance of stress cracking. By contrast, features having sharp transitions or edges are particularly prone to stress cracking.

In the interest of clarity, some of the above parameters reference “a radially outermost and/or axially uppermost extremity of the underlying base contour, corresponding to a junction between the base and a side wall of the self-standing container”. For most containers, this is where the base contour transitions to a generally upright sidewall. This may also correspond to a region of the container having the maximum circumference of the container, especially those having a substantially cylindrical side wall (although it will be appreciated that other shaped side walls having a substantially regular cross section are also possible).

However, the side wall of certain containers may have slight variations in cross section along their length. For example, the side wall may be ribbed at certain locations.

However, in the present context, a side wall is generally differentiated from the base by virtue of the volume of the side wall being substantially directly proportional to its axial length.

Advantageously, containers having a side wall of this type, especially those side walls that are substantially cylindrical, have better packing densities; multiple containers can be stood next to one another in a tightly packed matrix. Furthermore, such side walls conveniently support labels and other indicia.

In addition to the above, as the feet of the base are spheroidal, it will be understood that the contact of each foot with a planar surface on which the base can rest is via a convex surface. Preferably, contact between a given foot and that planar surface is via a contact point on the curved surface of that foot. By contrast, bases having feet with flat surfaces in contact with a planar surface are more susceptible to increases in pressure in that these flat surfaces can be more significantly deformed under pressure, for example where the feet are pushed outwards and downwards and no longer provide flat surfaces for the container to stand on.

To maximise the capacity and strength of the container while minimising material usage, the underlying base contour is preferably substantially hemispherical. The contour may be, for example, that of an oblate spheroid whose polar axis coincides with a central axis of the base. For similar reasons, the foot formations are suitably elongate, such as partial ellipsoids or prolate spheroids. In certain embodiments of the invention, the foot formations are ovoid (partially egg-shaped), in which case the contact points of the feet are most conveniently defined by the widest part of the cross-section of each foot formation being offset inwardly toward an inner end of the foot formation. In other words, the foot formations taper to a greater extent at their radially outer portions than their radially inner portions with respect to the central axis of the base.

Preferably, the base comprises formations, such as foot formations, whose shapes are substantially rotationally symmetrical about an axis. For example, shapes such as spheroids, ellipsoids and ovoids that define the foot formations are preferably substantially rotationally symmetrical about an axis. Advantageously, if these shapes that form the base are rotationally symmetrical, the material used to form these structures can be minimised and the internal capacity of the base can be maximised, as it is closer to an ideal spherical shape. At the same time the strength of the base can be maximised, since the smooth transition portions resulting from the spheroidal shapes involved in the design of the base minimise the stresses on the base.

To define feet with minimal usage of material, the elongate foot formations preferably have respective longitudinal axes, which axes lie in planes extending radially from a central axis of the base. Those axes of the foot formations suitably extend outwardly and upwardly in conical relation from the central axis of the base.

Each foot formation may have an elliptical, preferably ovate intersection with the underlying base contour. To reduce stress concentration, the intersection is preferably of concave cross section.

To strengthen the base, the foot formations preferably radiate from a stiffening formation disposed centrally between the feet. The stiffening formation may comprise a protrusion and/or a depression. Ideally, these respectively extend out from or extend in toward the base contour. The protrusion and/or depression may be, at least in part, approximately polygonal and the number of sides of the polygon may correspond to the number of foot formations.

Moreover, the stiffening formation may be in the form of a crater, for example comprising a central depression surrounded by a generally annular protrusion (or a central protrusion surrounded by a generally annular depression). Preferably, the depression and protrusion transition into one another. Ideally the stiffening formation is formed of concentrically arranged protrusions and depressions which are respectively convex and concave relative to the base—more specifically, to an exterior surface of the base.

The role of the stiffening formation can be all the more important the larger and further spaced the foot formations are from one another, especially for containers that are subject to significant internal pressures. A central region of the container encircled by the foot formations may bow out with sufficient super-atmospheric pressure, and this effect can be exacerbated when foot formations extend over a large area of the base. Notably, this is a problem circumvented by the container described in GB 2479451 by placing the foot formations close to one another. Advantageously, the concentric arrangement of protrusions and depressions of the stiffening formation significantly add stiffness to the base at this central region.

Generally, a sharper radius of curvature of and between concentric protrusions and depressions of the stiffening formation will result in a stiffer stiffening formation. However, this comes at the expense of the base being more vulnerable to stress cracking. Thus, in previously known bases, especially those having foot formations less spaced apart (e.g. such as that described in United Kingdom Patent No. GB 2479451) a gently curving transition between the foot formations and a central region are generally favoured.

However, it has been found that with the appropriate stretch blow moulding process, material distribution in the base can be made to automatically concentrate towards the central region of the base, reinforcing it, thereby offsetting the vulnerability to stress cracking introduced by the small radii or curvature. Thus, due to increased material thickness at the central region, the stiffening formation can be stiffer than otherwise without significantly exposing the base to stress cracking. It should also be noted that this concentration of material towards the central region is encouraged by a slower blowing process which is itself supported by the geometry of the base as defined by the above ratios.

The foot formations are suitably separated by valleys, which may radiate from the stiffening formation. To minimise material usage, the valleys preferably widen moving outwardly across the base. Each valley may, for example, have an inner and an outer section and the walls of the valley may diverge more sharply in the outer section than in the inner section. However, the walls of the valley may diverge in both the inner and the outer sections of the valley.

In plan view, each foot formation may have an enlarged central region from which the foot formation tapers inwardly across an inner portion to an inner end. In that case, the inner portions of the foot formations suitably lie in segmented relation around the base. To minimise material usage, it is preferred that in plan view, each foot formation tapers from the enlarged central region outwardly across an outer portion to an outer end of the foot formation.

As mentioned, the inventive concept extends to a container such as a keg or a bottle having the base of the invention. Preferably, the container is constructed from a preform, ideally via a stretch blow-moulding process. Ideally, the preform and the container are made of PET or a similar material. Thus, the inventive concept may also extend to a preform used to construct a container having the base of the first aspect of the invention.

As set out above, the improved base has many advantages including improved standing ability, resistance to stress cracking, lower material usage and others. Consequently, when using a standard preform in the construction of a container having such a base, it follows that the base may be “over-engineered”, for example, having a wall thickness which is greater than necessary. Whilst lower weight preforms can be used to realise lower material usage, an alternative way to benefit from the advantages of the base is to reallocate the material usage such that the material savings in the base are instead transferred to other parts of the container. Notably, containers that are subject to high internal pressure are vulnerable to bowing and bursting at the side wall. Accordingly, it can be beneficial to reallocate the material saving that is realised from the base to the side wall.

To facilitate this, a further aspect of the present invention is a preform for stretch blow-moulding into a container having a base, such as a base according to the first aspect of the invention. Ideally, the preform has a dome-shaped tip portion, a substantially cylindrical body portion and a neck portion, wherein the tip portion has a wall that is relatively thinner than the body portion. Generally, the tip portion corresponds to the part of the preform forming the base of the container, and the body portion corresponds to part of the preform forming the side wall of the container. Thus, material can be successfully redistributed from the base to the side wall of a container.

The Applicants have empirically determined that, in the construction of a container having a base such as that according to the first aspect of the present invention, a preform having characteristics defined by the ratio between any two or more of following parameters is particularly effective:

TABLE B Parameter Value P₁ - (Axial length of preform, including the neck portion, 123 the body portion and the tip portion) P₂ - (Approximate average diameter of bore of preform) 19.32 P₃ - (Wall thickness of body portion of preform) 3.88 P₄ - (Wall thickness of tip portion of preform) 2.7 P₅ - (Internal radius of curvature of tip portion of preform) 9.66 P₆ - (External radius of curvature at axial extremity of tip 12.36 portion of preform) P₇ - (Axial length of tip portion) 18

Ideally, a ratio between any two of: P₁, P₂, P₃, P₄, P₅, P₆ and P₇ can be derived by expressing the corresponding values in Table B as ratios of one another. Preferably, the value of each parameter P₁, P₂, P₃, P₄, P₅, P₆ and P₇ should be considered to be within a tolerance of ±5%, more preferably within a tolerance of ±2%.

Notably, the ratio of P₄:P₃: is 2.7:3.88 (or approximately 1:1.44). By contrast, in standard preforms, this ratio would be closer to 1:1.

It will be appreciated that the above features or advantages of different aspects of the invention may be combined or substituted where context allows. Furthermore, the features or advantages themselves may constitute further aspects of the invention.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 is an underneath plan view of a container having a petaloid base in accordance with a first embodiment of the invention;

FIG. 1a is a side view of the container of FIG. 1;

FIGS. 2A and 2B are sectional side views along the line B-B through the petaloid base of the container shown in FIG. 1;

FIG. 3 is a sectional side view along the line A-A through the petaloid base of the container shown in FIG. 1;

FIG. 4 is an underneath perspective view of the petaloid base of the container shown in FIG. 1;

FIG. 5 is an underneath plan view of a container having a petaloid base in accordance with a second embodiment of the invention;

FIGS. 6A and 6B are sectional side views along the line B-B through the petaloid base of the container shown in FIG. 5;

FIG. 7 is a sectional side view along the line A-A through the petaloid base of the container shown in FIG. 5;

FIG. 8 is a underneath perspective view of the petaloid base of the container shown in FIG. 5;

FIG. 9 is an underneath plan view of a container having a petaloid base in accordance with a third embodiment of the invention;

FIGS. 10A and 10B are sectional side views along the line B-B through the petaloid base of the container shown in FIG. 9;

FIG. 11 is a sectional side view along the line A-A through the petaloid base of the container shown in FIG. 9;

FIG. 12 is a perspective underneath view of the petaloid base of the container shown in FIG. 9;

FIGS. 13 to 21 are charts depicting the result of tests carried out on containers having base designs relating to both the prior art, and various embodiments of the present invention;

FIG. 22 is an underneath plan view of a container having a petaloid base in accordance with various embodiments of the invention;

FIGS. 23 and 24 are perspective cutaway views of prior art bases;

FIG. 25 is a side view of a container having the prior art base of FIG. 24;

FIG. 26 is a cross sectional view of a non-standard preform for use in stretch blow-moulding a container having a base according to the present invention; and

FIG. 27 is an enlarged partial view of FIG. 26.

FIG. 1 is an underneath plan view of a container 10 having a petaloid base 14 in accordance with a first embodiment of the invention. The container comprises a hollow body of blow-moulded PET. The body of the container 10 is approximately of circular horizontal section, the radius of that circle extending orthogonally from a central longitudinal axis 12 that extends centrally through the closed base 14 of the container 10. It should be noted that the term “central longitudinal axis” is used herein as a general reference feature for both the container 10 as a whole and the petaloid base 14 in isolation, even if the base 14 in isolation is not necessarily elongate along that axis 12.

Referring to FIG. 1a , which is a side view of the container of FIG. 1, above the base is a side wall 48 surmounted by a neck portion 50, as is known in the art. The side wall 48 is integral with and terminates at its lower end in the base 14; in turn, the side wall 48 is integral with and terminates at its upper end in the neck portion 50 near the top of the container. As is the case with many other drawings herewith FIG. 1a includes dimension information in millimetres. Thus, for example, it can be seen that the base 14 has an axial height of 28 mm, and a maximum diameter of 65.5 mm.

The side wall 48 comprises a central cylindrical section which has an axial height of 77 mm. Thus, the side wall 48 is cylindrical over the majority of its axial length, with the diameter of that cylinder (64 mm) being slightly smaller than its maximum diameter (65.5 mm). Axially above and below the cylindrical section, the side wall tapers outward to its maximum diameter. Advantageously, this cylindrical section of the side wall 48 can conveniently support labels and other indicia, yet the tapering introduces strengthening ribs to the side wall. The maximum diameter of the side wall 48 matches the maximum diameter of the base 14.

The fundamental or underlying shape of the base 14 is a slightly flattened hemisphere, that hemisphere being rotationally symmetrical about the central longitudinal axis 12 of the container 10. More generally, the underlying shape of the base 14 is an oblate spheroid, being a rotationally symmetric ellipsoid having a diameter on its polar axis (coinciding with the central longitudinal axis 12) that is shorter than the diameter of the equatorial circle whose plane bisects it. This approximately hemispherical shape maximises resistance to internal pressure, reduces stress concentrations to resist cracking, and also maximises internal volume while minimising material usage.

In accordance with the invention, the base further includes integrally-moulded blister-like feet 16 disposed in a petaloid arrangement around the base 14. The feet 16 are defined by five hollow ovoid foot formations 16 that radiate equi-angularly from a relatively shallow stiffening formation 18 substantially centred on the central longitudinal axis 12.

Referring to FIG. 4, which shows an underneath perspective view of the petaloid base 14, the stiffening formation 18 is broadly crater-shaped, with a central depression 18 a surrounded by a broadly annular protrusion 18 b, both of which are centred on the central longitudinal axis 12.

In alternative embodiments, the stiffening formation may take other forms—for example, a central depression without an annular protrusion, or a central protrusion optionally with an annular depression.

Referring to FIG. 3, in which is shown a sectional side view along the line A-A through the petaloid base 14 of the container shown in FIG. 1, the foot formations 16 are generally elongate ellipsoids in the form of prolate spheroids, a prolate spheroid being a spheroid whose diameter along its polar axis is greater than its equatorial diameter.

It should be noted that the general term “prolate sphereoid” used herein includes shapes that may deviate slightly from a true spheroid. For example, the term may include top-shaped formations some of which have the appearance of true prolate spheroids that are stretched to a point along the polar axis, and/or which may have concave regions.

Referring to FIGS. 2A and 2B, which are views taken through the cross-section plane B-B shown in FIG. 1, the polar axes 20 of the spheroidal foot formations 16 extend outwardly and upwardly in equi-angularly spaced radially-disposed planes from the central longitudinal axis 12 of the container 10. Thus, the polar axes of the foot formations 16 lie on a virtual frusto-conical surface surrounding the central longitudinal axis 12.

Referring back to FIG. 1, circumferentially adjacent pairs of foot formations 16 are separated by valleys 22 that radiate equi-angularly from regions 24 adjacent to the stiffening formation 18. The valley floors follow the spheroidal shape of the base and open at their outer ends to an outer portion of the base that lies radially outwardly beyond the foot formations 16. Furthermore, each foot formation 16 and the stiffening formation 18 are joined via a transition portion.

Referring back to FIG. 3, the radius of curvature r of the concave central depression 18 a is smaller than the general radius of curvature R of the spheroidal base: thus R>r. Also, the concave central depression 18 a extends to a level within—and thus, in use, above—the lowermost apex of the underlying base contour.

In contrast, the annular protrusion 18 b extends to a level beyond—and thus, in use, below—the lowermost apex of the underlying base contour. The radius of curvature of the peak of the annular protrusion 18 b is 1 mm, as indicated by the reference numeral “R1”. Other radii values are indicated in a similar manner.

Referring to FIGS. 1 and 4, the foot formations 16 bulge outwardly from the underlying spheroidal contour of the base 14 by virtue of an ovoid convex wall. The convex wall of each foot formation is surrounded by a concave transition zone 26 in the shape of an ovate ring. The transition zone extends smoothly into the spheroidal wall of the base with a large radius of curvature to reduce stress concentration and hence to minimise stress cracking. The transition zones 26 of circumferentially adjacent foot formations partially define the valley 22 between those foot formations.

Each foot formation 16 is generally elliptical (in example, ovate) in underneath plan view, reaching a maximum width in an enlarged central region between its inner end and its outer end. Thus, each foot formation 16 tapers in opposite directions from the widest part of the central region: along an inner portion moving inwardly toward the central longitudinal axis 12 to the inner end; and along an outer portion 36 moving outwardly away from the central longitudinal axis 12 to the outer end.

In underneath plan view, the inwardly-tapering inner portions 34 of the foot formations fit closely between their neighbours around the circular base like segments of an orange. These inner portions 34 of the foot formations 16 alternate with, and are separated by, narrow inner sections of the valleys, which may be approximately parallel but, in this example, widen slightly as they extend outwardly from the stiffening formation 18. However where they extend outwardly into their outer sections beyond the widest part of the foot formations, the valleys widen near-exponentially between the tapering outer portions of the foot formations 16 until they reach a maximum width between the outer ends of adjacent foot formations.

Thus, moving along the valleys from the central longitudinal axis toward the outer diameter of the base, the gap between the foot formations increases. By contrast, in a previously known petaloid base, such as that disclosed in EP 0671331, this gap decreases.

Referring to FIG. 3, the foot formations 16 extend to a level beyond—and thus, in use, below—the lowermost apex of the base 14 as defined by the annular protrusion 18 b of the stiffening formation 18. The foot formations 16 all extend to the same level. Thus, at that level, each foot formation defines a contact point 42 that will lie stably upon a flat support surface (not shown) orthogonal to the central longitudinal axis 12 of the container 10.

The contact points 42 of the foot formations 16 are equi-spaced on and around a contact circle centred on the central longitudinal axis of the container. The diameter (x) of the contact circle relates to the side wall diameter (Dy) of the container in a ratio as follows:

$\frac{Dy}{0.5\; x} = k$

In the present embodiment, the diameter (Dy) of the side wall can be seen in FIG. 1 to be 65.5 mm. The diameter (x) of the contact circle can be determined from FIG. 3 to be 40 mm. Therefore, in the present embodiment, the specific value of k is 3.275.

However, for the invention in general, k can preferably be between 3.0 and 3.6, more preferably between 3.1 and 3.5, still more preferably between 3.2 and 3.4 and typically 3.275. These values may be contrasted with the base of GB 2479451, which preferably has a k value of between 3.6 and 5.5, typically 4.7.

Nonetheless, a central area within the contact circle between the contact points of the foot formations benefits from the rigidity imparted by the stiffening formation. Moreover, the stiffening formation, in cooperation with the foot formations, resists movement caused by internal super-atmospheric pressure, up to burst pressure. The rigidity of the area within the contact circle is further enhanced by the undulating wall section defined by the inner portions of the foot formations, the valleys between them, and the stiffening formation 18.

Stiffness within the contact circle is important not just for a high burst pressure but also for stability. This is because the lowest point inside the contact circle, defined by the annular protrusion 18 b of the stiffening formation 18, will tend to be pushed down under internal pressure. If that lowest point moves so far as to contact a supporting surface in use, the container cannot rest stably on the contact points of the foot formations. The stiffness of the base shape of the invention means that the distance from the lowermost point of the base 14 within the contact circle to a supporting surface can be relatively small, to the benefit of stability and capacity relative to the height of the container 10. As depicted in FIG. 3, this distance is 2 mm.

Referring to FIGS. 2A and 2B, viewing any one foot formation 16 end-on (i.e., from the side of the container looking inwardly towards the central longitudinal axis), the contour of that foot formation describes a substantially constant convex radius between the concave radii of the transition zones to each side.

Referring to FIG. 23, which is a perspective view of a conventional petaloid base, a conventional petaloid base typically has flatter surfaces defining a V-shaped valley between the feet, to the detriment of material usage and stress concentration. Stress concentrations create areas of a container that are particularly vulnerable to rupture under high internal pressure.

FIGS. 5 to 8 and 9 to 12, respectively, show base designs corresponding to second and third embodiments of the invention. These embodiments share the same key features as described above in relation to the first embodiment. Thus, in the interest of brevity, mainly the differences from the first embodiment will be described hereinafter. If referenced, corresponding features are identified by the same reference numerals.

The second embodiment, corresponding to FIGS. 5 to 8, relates to a container 10 of a larger size and volume than the first embodiment. For example, as can be seen in FIG. 5, the side wall diameter (Dy) is 94 mm. The third embodiment, corresponding to FIGS. 9 to 12, relates to a container 10 of an even larger size and volume than the first and second embodiments; as can be seen in FIG. 9, the side wall diameter (Dy) in this case is 298 mm.

Nonetheless, these three embodiments have substantially the same k value of 3.275 and are broadly have the same proportions. Accordingly, a set of ratios can be determined that apply to all three embodiments.

For example, considering that each foot formation 16 has an elliptical intersection with the underlying base contour, and that elliptical intersection defines a transition between the underlying base contour and a foot formation, a ratio of D₂:D₁ may be calculated, where:

-   -   D₁ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the underlying base contour,         corresponding to a junction between the base and a side wall of         the self-standing container; and     -   D₂ is a radial distance from the central longitudinal axis to a         radially outermost extremity of the transition.

Referring to FIG. 1, D₁ is half of the diameter Dy and so equal to 32.75 mm, and D₂=31 mm. Thus the ratio can be expressed as 31:32.75 or 1:1.056 (accurate to three significant figures). Referring to FIG. 5 a broadly equivalent ratio of 44.5:47 can be obtained from the corresponding values of D₂ and D₁. Referring to FIG. 9, again, a broadly equivalent ratio of 141:149 can be determined.

Additional ratios can be calculated from other parameters depicted or calculable from the Figures. For example, for any one embodiment, a ratio between any two of: D₁, D₂, D₃, D₄, D₅, D₆, D₇, D₈, D₉, D₁₀, D₁₁, R_(A), R_(B), R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) can be derived by expressing the corresponding values as ratios of one another. For clarity, some of these parameters are depicted generically in FIG. 22 without measurement data included.

As set out above, D₁ is a radial distance from the central longitudinal axis 12 to a radially outermost extremity of the underlying base contour, corresponding to a junction between the base 14 and a side wall 48 of the self-standing container 10. Thus for the first embodiment shown in FIGS. 1-4, the value of D₁ is 32.75, for the second embodiment shown in FIGS. 5-8 the value of D₁ is 47, and for the third embodiment shown in FIG. 9-12 the value of D₁ is 149. The values for D₂, D₃, D₄, D₅, D₆, D₇, D₈, D₉, D₁₀, D₁₁, R_(A), R_(B), R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) are in millimetres, and these are shown in, or are derivable from the drawings wherein:

-   -   D₂ is a radial distance from the central longitudinal axis 12 to         a radially outermost extremity of the transition (e.g. shown in         FIG. 1 as 31 mm);     -   D₃ is the radial distance between the central longitudinal axis         and a radially inner end of a foot formation (e.g. shown in FIG.         1 as 6 mm);     -   D₄ is the radial distance between the radially inner end of a         foot formation, and radially outermost extremity of the         transition (e.g. corresponding to the difference between D₂ and         D₃=25 mm);     -   D₅ is the widest distance between two points on a foot formation         which are radially equidistant from the central longitudinal         axis and which do not form part of the transition (e.g. shown in         FIGS. 1 and 2B as 12.5 mm);     -   D₆ is the widest distance between two points on the transition         which are radially equidistant from the central longitudinal         axis (e.g. shown in FIGS. 1 and 2B as 18.6 mm);     -   D₇ is the radial distance between the central longitudinal axis         and a contact point 42 of a foot formation (e.g. shown in FIG. 1         as 20 mm);     -   D₈ is the axial distance between a planar surface on which a         foot formation rests (i.e. at the contact point) when standing         and the radially outermost, axially uppermost extremity of the         underlying base contour, corresponding to a junction between the         base 14 and a side wall 48 of the self-standing container 10         (e.g. shown in FIGS. 1a and 3 as 28 mm);     -   D₉ is the axial distance between a planar surface on which a         foot formation 16 rests when standing and the radially         outermost, axially uppermost extremity of the transition (e.g.         shown in FIG. 2B as 19.2 mm);     -   D₁₀ is the axial distance between a planar surface on which a         foot formation 16 rests when standing and a line, parallel to         that planar surface that passes through the two points on the         transition which are the furthest apart from one another, and         also radially equidistant from the central longitudinal axis 12         (e.g. shown in FIG. 2B as 9.4 mm);     -   D₁₁ is the axial distance between a planar surface on which a         foot formation rests when standing and a line, parallel to that         planar surface that passes through the two points on the foot         formation which are the furthest apart from one another, and         also radially equidistant from the central longitudinal axis,         but do not form part of the transition (e.g. shown in FIG. 2B as         5.4 mm);     -   R_(A) is the radius of curvature of a foot formation within a         section plane intersecting a contact point 42 of the foot         formation, the section plane being parallel to and radially         spaced (by distance D₇) from the central longitudinal axis 12.         Ideally, R₁ is the radius of curvature at the contact point 42         (e.g. shown in FIG. 2A as 6.3 mm);     -   R_(B) is the radius of curvature of the transition within a         section plane intersecting a contact point 42 of the foot         formation 16, the section plane being parallel to and radially         spaced (by distance D₇) from the central longitudinal axis (e.g.         shown in FIG. 2A as 6.3 mm);     -   R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I) are radii of         curvature measured within a section plane parallel with and         intersecting both the central longitudinal axis 12 and a contact         point 42 of the foot formation 16 with:         -   R_(C) being the radius of curvature of the underlying base             contour between a radially outermost extremity of the             underlying base contour and a radially outermost extremity             of the transition (e.g. as shown in FIG. 3 as 21 mm);         -   R_(D) being the radius of curvature of the transition             between the base contour and a radially outermost extremity             of the foot formation (e.g. as shown in FIG. 3 as 3.6 mm);         -   R_(E), R_(F), R_(G) being the radii of curvature of the foot             formation taken at approximately equi-spaced intervals             between the radially outermost extremity of the foot             formation and the contact point, with R_(E) being the radius             of curvature closer to the radially outermost extremity of             the foot formation (e.g. as shown in FIG. 3 as 189 mm),             R_(G) being the radius of curvature closer to the contact             point 42 (e.g. as shown in FIG. 3 as 8.9 mm), and R_(F)             being the radius of curvature of the foot formation 16             between R_(E) and R_(G) (e.g. as shown in FIG. 3 as 9 mm);         -   R_(H) being the radius of curvature of the foot formation 16             at the contact point (e.g. as shown in FIG. 3 as 11.7 mm);             and         -   R_(I) being the radius of curvature of the foot formation             radially between the contact point and the central             longitudinal axis (e.g. as shown in FIG. 3 as 24.8 mm);

It should be noted at all the above-referenced radial distances are measured along a plane to which the central longitudinal axis is perpendicular. Similarly, axial distances are measured along an axis perpendicular to that plane.

By comparing the values provided in the drawings of the various embodiments, various ratios corresponding to the general invention can be determined. Nonetheless, for completeness, radius and distance data for each of the three base designs illustrated in FIGS. 1 to 4, 5 to 8 and 9 to 12, respectively, are given below in Table 2 and 3. These are given with looser definitions than those used to define D₁, D₂, D₃, D₄, D₅, D₆, D₇, D₈, D₉, D₁₀, D₁₁, R_(A), R_(B), R_(C), R_(D), R_(E), R_(F), R_(G), R_(H) and R_(I), but correspond in many cases to the same parameter:

TABLE 2 Radius data for the base designs illustrated in FIGS. 1-4, 5-8 and 9-12 Base of Base of Base of RADIUS DATA FIG. 1-4 FIG. 5-8 FIG. 9-12 Radius of concave central 1.0 mm  1.0 mm  1.0 mm depression Radius of a foot formation at 24.8 mm  35.6 mm 112.8 mm  a position on the central region between the contact circle and the inner portion Radius of a foot formation at 11.7 mm  16.8 mm 53.2 mm a position on the central region that is radially outer of and adjacent to the contact circle Radius of a foot formation at 8.9 mm 12.8 mm 40.5 mm a position on the central region between the contact circle and the outer portion Radius of a foot formation at 9.0 mm 12.9 mm 41.0 mm a position on the outer portion between the radially outer end and the central region of the foot formation Radius of a foot formation at 189.0 mm  271.2 mm  860.0 mm  a position on the outer portion adjacent the radially outer end of the foot formation Radius of concave transition 3.6 mm  5.2 mm 16.4 mm zone between underlying base contour and radially outer end of a foot formation Radius of transition from 21.0 mm  30.1 mm 95.5 mm underlying base contour to side wall

TABLE 3 Distance data for the base designs illustrated in FIGS. 1-4, 5-8 & 9-12 Base of Base of Base of DISTANCE DATA FIG. 1-4 FIG. 5-8 FIG. 9-12 Distance along central longitudinal  2.0 mm  2.5 mm  5.4 mm axis between convex central depression and plane containing the contact circle Distance along axis aligned with  2.5 mm  3.6 mm  11.4 mm central longitudinal axis from transition zone (between central depression and a foot formation) to plane containing the contact circle Axial depth of the base portion 28.0 mm 40.2 mm 127.4 mm (i.e. axial distance from plane containing the contact circle to axially lower end of cylindrical side wall) Radial length from central 31.0 mm 44.5 mm 141.0 mm longitudinal axis to transition between base contour and foot formation

All of the embodiments 1 to 3, shown respectively in FIGS. 1 to 4, 5 to 8 and 9 to 12 have the substantially the same ratio values. However, it will be apparent to a person skilled in the art that there may be variation in these and other values. For example, as a rule of thumb, a tolerance of ±3 to 5% of the stated or calculated value may be possible. In general, these values, ratios and features of the petaloid base of embodiments of the invention can be applied or adapted to a wide range of containers.

For example, whilst FIGS. 1 to 12 show five-footed bases of the invention, other variations are possible without departing from the inventive concept. For example, the base of the invention may have seven foot formations instead of five. An odd number of feet is preferred for optimum stability, there being at least three feet, but preferably not more than seven feet; five or seven feet are considered optimal.

Further, the petaloid base of the invention may be applied to bottles that usually have relatively small capacities (of 0.33 litres, 0.5 litres, 1 litre, 1.5 litres or larger) which are typically used for carbonated soft drinks, or for relatively larger kegs (of a capacity of 15-30 litres and larger) which are typically used for the distribution and dispensing of beer.

However, regardless of the size of the container, the present invention is particularly suited to applications in which there is a super-atmospheric internal pressure. Notably, the softly-curving shape of the base with an absence of sharp radii is beneficial to resist stress cracking. Also, while the base has a thinner wall, it is just as strong, if not more strong, than existing base designs. A strong base is particularly important in applications where the containers are subjected to elevated internal pressure and/or elevated temperature, such as the use of carbonated soft drinks, beer and hot-fill or pasteurised liquids.

Furthermore, the present invention is also advantageous for applications where a pressurised gas is used to extract beverage from the container via a dip-tube, as is common with kegs. Specifically, the distance from the lowermost point of the base within the contact circle to a supporting surface is relatively small compared to prior known designs. As a result, the arrangement of the base of the present embodiment is particularly suited to containers for dispensing liquids under pressure because the quantity of beverage that can be practically dispensed from the container can be maximised.

In this context, the container may be used as a beer keg that is provided with a closure assembly that is sealed on to the tubular neck of the keg in a push-fit arrangement. A dip-tube is coupled to the closure assembly (not shown) and extends from it along the central longitudinal axis into the base of the keg. The axially lower end of the dip-tube extends at least to the stiffening formation.

In use, when dispensing a beverage, the keg is maintained in an upright position. The closure assembly allows a pressurised gas to be introduced into the headspace of the keg to force the beverage out through the dip-tube. As the axially lowermost end of the dip-tube may be located at a relatively low axial position within the keg, this ensures that almost all of the beverage within the keg can be extracted from it.

It may be possible to further increase the amount of beverage that can be practically extracted from the keg by extending the tube into one of the foot formations. In such an arrangement, the tube would need to bend away from the central longitudinal axis at its lower end. Although this may marginally increase the amount of beverage that can be dispensed from the keg, this can complicate process of fitting the closure assembly and tube to the keg. In particular, inserting a bent tube into the keg can require a complicated automated fitting process. Furthermore, the bending of the tube away from the central longitudinal axis can subject the closure assembly to which the tube is attached at its axially upper end to uneven forces. This can reduce the reliability of the closure assembly, which is of particular concern when the keg is subject to high internal pressure.

Experimental Data

To further put the invention into context, but without limiting its broadest scope as defined in the claims, a series of example test results will now be described with reference to FIGS. 13 to 21. These tests were carried out on various base designs relating to various embodiments of the present invention.

With respect to the foregoing Tables 4 and 5, and FIGS. 13 to 21, the data provided is categorised by the following bottle and base designs:

-   -   (i) ‘0.5 I Std ref’;     -   (ii) ‘0.5 I Petainer base’; and     -   (iii) ‘0.5 I ISF base’.

These terms to relate to:

-   -   (i) a bottle with a volume of 0.5 litres with a standard base         design, as depicted in FIG. 23;     -   (ii) a bottle as depicted in FIG. 25 with a volume of 0.5 litres         with a base design according to GB 2479451, as depicted in FIG.         24; and     -   (iii) a bottle with a volume of 0.5 litres with a base design         according to the present invention, and as shown in FIG. 1 a.

It should be noted, with reference to FIG. 1a that the actual capacity of the bottle denoted as “0.5 I ISF base” is greater than half a litre exactly. More precisely, this container has a brim-full capacity of 523 ml, with the “Fill-point” of 500 ml being shown to be 42 mm below the brim of the bottle.

It should also be noted that the following experimental data includes further parameters associated with the container of the first embodiment. Whilst it may not necessarily be possible to express these parameters as ratios, the relationship between the different parameters can be used to characterise the container of the first embodiment, and so the invention in general.

Furthermore the data provided is also categories with respect to an ‘original process’ and a ‘low weight process’.

The original process is a standard blow moulding process for producing 0.5 litre bottles. The minimum wall thickness required at the standing surface of the feet using this kind of process is 0.25 mm. As can be seen from Table 4 below, in the original process, the base of GB 2479451 and that of the present invention both gave savings in terms of base material when compared to the standard reference bottle due to their designs. For example, the base of GB 2479451 gave a weight reduction of 0.31 g when compared to the standard reference bottle. The base of the present invention (‘0.5 I ISF base’) gave a weight reduction of 0.34 g when compared to the standard reference bottle.

The low weight process is a blow moulding process for producing bottles, where the amount of base material is reduced and can therefore be moved into other parts of the bottles, for example, the side wall. The low weight process was set up so that there was just enough force in the blowing process to blow the standard reference bottle.

During production control, bottles are normally cut at a certain height from the standing surface to obtain various measurements, for example, wall thickness and weight. Due to its shape, the base design of the present invention does not hold the same volume of water at a specified height as existing base designs. In order to provide the best comparison between the base of the present invention and existing bases, the bottles of the present invention were instead cut at the point where they contained approximately the same volume of water as existing bases. In this regard, the column entitled ‘Volume (ml)’ refers to the point at which each base was cut in terms of its volume rather than its height.

TABLE 4 Comparison of the effect of the original process and the low weight process on the weight of bottles with different base designs Weight Weight reduction Weight reduction (g) (original − Base Volume of base per process low weight Process design (ml) (g) (g) process) Original 0.5 | Std ref 58.61 5.47 0.00 process 0.5 | 58.62 5.16 0.31 Petainer base 0.5 | ISF 59.33 5.13 0.34 base Low 0.5 | Std ref 58.90 3.50 0.00 weight 0.5 | 58.63 3.04 0.46 2.43 process Petainer base 0.5 | ISF 58.00 2.98 0.52 2.49 base

As can be seen from Table 4, the low weight process gives a significant saving in materials. However, as will be seen from the following description, in spite of this saving in material usage, the strength of each of the bottles/bases of the invention is not compromised.

Furthermore, the base of the present invention has a fairly similar weight to that of GB 2479451. It can be seen from the results in Table 4 that approximately 2.5 g of material has been moved from the base to other parts of the container in present invention using the low weight process.

FIG. 13 shows the results of a series of ‘fill level drop’ tests. A fill level drop test is a form of thermal stability test showing the degree to which a bottle deforms under pressure and/or elevated temperature. Therefore, this test gives an indication of a bottle's strength under such conditions.

The fill level value is the measurement of the height from the seal surface to the fill level of the liquid in the container. The fill level drop is the difference in the starting fill level measurement to the fill level measured after the specified pressure and/or temperature conditions have been applied and the fill level drop values in FIG. 13 are given in millimetres (mm).

Under pressure and/or elevated temperature, the diameters and/or height of the containers and a drop in the lowermost level of the base gives the fill level drop. The overall bottle expansion may be calculated using the fill level drop measurements.

The same preform was used for all trials, namely a standard 24 g one-way preform. An existing standard 0.5 litre one-way bottle mould was used as a reference. The different base designs were used on the existing bottle blow moulds. Eight original 0.5 litre blow moulds and one with a base corresponding to that of GB 2479451 and one with the base design of the present invention were fitted into the blow machine.

As can be seen from FIG. 13, measurements were taken for both the original process and the low weight process at 22° C. and 38° C. The empty bottles were measured before being filled with carbonated water. Once the bottles were filled, an initial fill level measurement was taken. For carbonated soft drinks, the level of carbonisation is normally at around 8 g of CO₂/l and this was used here.

The bottles were then placed in 22° C./50% Relative Humidity for 24 hours and the fill level was measured again and the fill level drop was calculated. Subsequently, the bottles were placed in 38° C./50% Relative Humidity for 24 hours and the fill level was measured a third time and the fill level drop was calculated again. The results are illustrated in FIG. 13.

As can be seen from FIG. 13, the fill level drop was lowest for the ‘0.5 I ISF base’ (the base of the present invention) in both the original process and the low weight process at both 22° C. and 38° C. This shows that the bottles using the base of the present invention deformed the least under pressure and/or elevated temperature. The container and base of the present invention therefore has advantages over existing container and base designs.

FIG. 14 shows the results of a series of base decrease tests, with conditions corresponding to those used in the fill level drop tests of FIG. 13. Base decrease tests indicate the degree to which a base has deformed and/or expanded due to the heat and pressure conditions used. It is clearly disadvantageous if the middle of the base is pushed downwards under pressure, such that it projects to a level lower than the feet of the base, as this causes the container to rock on the centre of the base rather than standing properly on its feet.

As can be seen from FIG. 14, the base of the present invention showed the least significant base decrease for the low weight process and is thus advantageous over both the standard base design and the base design according to GB 2479451. The base of the present invention therefore offers better standing stability compared with existing base designs.

FIG. 15 shows the results of a series of base clearance tests for each of the different base designs in both the original and low weight processes, with conditions corresponding to those used in the tests of FIGS. 13 and 14.

The base clearance is the vertical distance measured from the standing surface of the feet to just beside the injection point. This value may be used to see if the bottles will be unstable when the lowest point is not the feet but in the middle of the base. The results of the base clearance tests are from the same experiments as the base decrease tests.

As can be seen from FIG. 15, the base design of the present invention provides base clearance values that are comparable with those of the base design of GB 2479451. Thus, the base of the present invention has a very good standing stability.

FIG. 16 shows the expansion of each bottle in terms of their diameters at different heights along the bottle (i.e., 28.8 mm, 80 mm and 118 mm) for each of the different base designs in both the original and low weight processes.

As can be seen from FIG. 16, the base of the present invention has comparable results to that of GB 2479451. Thus, the base of the present invention is able to withstand changes in pressure and/or temperature very well.

FIG. 17 shows the expansion of each bottle in terms of height each of the different base designs in both the original and low weight processes.

As can be seen from FIG. 17, the base design of the present invention provides the smallest expansion in height. Thus, the base of the present invention is able to withstand changes in pressure and/or temperature better than existing base designs.

FIG. 18 shows the wall thickness for each bottle for each of the different base designs in both the original and low weight processes at standard temperature and pressure.

The wall thickness is measured at different heights calculated from the base (or from the surface on which the bottle is standing) and each wall thickness value is an average measurements made at a specific height at different parts of the container. The wall thickness at the standing surface is an average measured at the lowest point in each foot.

The blow force used in the original process caused the feet of the standard bottle to become overstretched and appear white. The wall thickness of the feet at the standing surface was 0.15 mm for the standard bottle, which is far below the required wall thickness for that type of bottle. As a result, the feet were very easily dented and the container with this base had poor standing instability.

The low weight process also caused the wall thickness of the standing surface of the feet of the base of the present invention to be lower than in the original process. However, due to the rounded design of the feet of the present invention, a wall thickness of 0.25 mm is not required to avoid overstretching and/or dented feet corners.

Thus, the low weight process is beneficial in combination with the design of the feet of the base of the present invention. As a result of the lower wall thickness, the base of the invention has base material savings. The low weight process is therefore an improved blowing process, as it decreases the amount of material required in the base.

TABLE 5 Comparison of the wall thickness at different bottle heights for bottles with different base designs Wall Wall Wall Wall thickness Base thickness thickness thickness (standing Process design (118 mm) (80 mm) (28.8 mm) surface) Original 0.5 | Std ref 0.26 0.27 0.31 0.24 process 0.5 | 0.27 0.29 0.29 0.44 Petainer base 0.5 | ISF 0.26 0.28 0.30 0.29 base Low 0.5 | Std ref 0.32 0.33 0.29 0.15 weight 0.5 | 0.33 0.35 0.25 0.31 process Petainer base 0.5 | ISF 0.33 0.33 0.26 0.18 base

The values in Table 5 are illustrated in FIG. 18. As can be seen from Table 5 and FIG. 18, the difference in wall thickness at height 118 mm and 80 mm shows that the material has been moved from the base upwards along the bottle to the side wall. This increase in wall thickness in the main body and/or neck of the bottle helps the bottle to withstand expansion better than in the original process.

FIG. 19 shows the results of an Accelerating Stress Cracking Test (ASCT), which is used to test the base of a bottle for resistance to cracking. This test can be performed in different ways. One way of performing the ASCT is to fill the bottles with carbonated water and put them in a sodium hydroxide (NaOH) bath. As the bottles expand, the internal pressure of the bottles decreases. The way that the ASCT is performed in the present invention is to maintain a high pressure during the whole test. The bottles are placed in a cup covering the base in burst tester apparatus. The bottles are filled with water and put under a constant pressure of 5 bars during the entire test. After 5 minutes, a solution of 0.2%+/−0.02% NaOH is poured into the cup, covering the entire outside of the base structure. The time until the bottles crack or starts to slowly leak, is measured.

The result of the ASCT depends on the base design and on the material distribution in the container. Standard bottle/base designs often crack during this test in less than 5 minutes. However, as can be seen from FIG. 19, the maximum time observed here was 20 minutes. The base design of the present invention performed just as well as the base according to GB 2479451, despite the fact that it has a smaller wall thickness. The base of the present invention is therefore more resistant towards stress cracking than existing base designs.

FIG. 20 shows a bottle verification top load and perpendicularity. The different base designs have little impact on the axial top load for empty bottles. The perpendicularity is slightly improved on the new design compared to the base of GB 2479451, but all values are inside specifications.

As can be seen from the data given above, the present invention provides advantages in container and base design. For example, the blow moulding process window has been improved, allowing such benefits as easy to use preforms with different r-PET levels, of different age and with different moisture levels. It is also easier to blow challenging bottle designs. Furthermore, it is possible to use lower blow pressure and still get good results. This allows savings in energy consumption and CO₂ footprint.

The results of standard tests (e.g., THS, ASCT burst pressure, drop test and top load) for analysing bottles shown for the present invention are equal or improved to those for existing bottle/base designs.

FIG. 21 shows a bar chart indicating the results of a series of burst tests by applying pressure to the different designs. The pressures shown in the bar chart of FIG. 21 relate to the pressures at which the different designs burst.

FIG. 21 shows that the base design of the invention performs in a similar manner to the base of WO 2007/064277 in both the original process and the low weight process.

In summary, the base of the present invention requires less material than existing base designs, while still performing very well in terms of strength and stability. In this regard, the container strength is maintained even though the weight of the base has been reduced by approximately 25% (e.g., see Table 4).

Furthermore, the base of the present invention is significantly more processing-friendly in the preform-to-bottle blowing process compared with existing base designs. The required blowing pressure to form the base of the present invention base during the blowing process can be lowered significantly to save energy.

As mentioned, the foregoing experimental data includes parameters the interrelationship between which can characterise the container of the first embodiment, and so the invention in general. By way of example, the volume to weight ratio of the 0.5 I Petainer base, and the 0.5 I ISF base can be determined and compared:

TABLE 6 Ordinary process Low weight process 0.5 | 0.5 | 0.5 | 0.5 | HALF LITRE BOTTLES Petainer ISF Petainer ISF (^(~)+3.5% headspace volume) base base base base Brimful volume of bottle (ml) 522 525 522 526 Total height of bottle (mm) 220 220 220 220 Fillpoint to 500 ml from base 181 178 181 178 height of base (where sidewalls 28 28 28 28 become parallel) diameter of contact circle 31.2 40 31.2 40 diameter of sidewalls (where 65.5 65.5 65.5 65.5 sidewalls become parallel) volume of base (ml) 58.62 59.33 58.63 58 corresponding weight of base (g) 5.16 5.13 3.04 2.98 volume to weight ratio (ml/g) 11.36 11.57 19.29 19.46

One way to benefit from the advantages of the base is to encourage reallocation of the material usage such that the material savings in the base are instead transferred to other parts of the container. Notably, containers that are subject to high internal pressure are vulnerable to bowing and bursting at the side wall. Accordingly, it can be beneficial to reallocate the material saving realised from the base to the side wall.

To facilitate this, a non-standard preform 100 may be used, as shown in FIG. 26.

The preform 100 comprises a dome-shaped tip portion 110, a substantially cylindrical body portion 120 and a neck portion 130. An enlarged view of the tip portion 110 is shown in FIG. 27. Dimensional values are included in FIGS. 26 and 27.

The tip portion 110 has a wall that is relatively thinner than the body portion 120. Thus, unlike a standard preform, stretch blow-moulding the preform into a container encourages redistribution of material from the base of the container to the side wall of a container.

This preform weighs 40.1 g, and so relates to containers of larger size than those used in the above-mentioned test. However, the relative distribution and arrangement of the features of this preform can be applied to a variety of different containers. Thus, in the construction of a container having a base such as that described in the first, second and third embodiments, a preform having characteristics defined by the ratio between any two or more of following parameters is particularly effective:

TABLE B Parameter Value P₁ - (Axial length of preform, including the neck portion, 123 the body portion and the tip portion) P₂ - (Approximate average diameter of bore of preform) 19.32 P₃ - (Wall thickness of body portion of preform) 3.88 P₄ - (Wall thickness of tip portion of preform) 2.7 P₅ - (Internal radius of curvature of tip portion of preform) 9.66 P₆ - (External radius of curvature at axial extremity of 12.36 tip portion of preform) P₇ - (Axial length of tip portion) 18

The above embodiments of the invention are described for the purposes of illustrating the invention only and are not to be read as limiting the scope of the invention, which is defined by the appended claims.

In summary, the base design of the present invention has clear advantages over existing base designs. For example, compared with the design of GB 2479451, the base design of the present invention generally has a lower weight, a better resistance to deformation, and better stability, especially under elevated temperature and internal pressure. 

1. A petaloid base for a self-standing container, the base having a central longitudinal axis, a spheroidal underlying base contour, and a plurality of spheroidal foot formations that interrupt and project from the underlying base contour to define a corresponding plurality of feet, wherein: each foot formation has an elliptical intersection with the underlying base contour, the elliptical intersection defining a transition between the underlying base contour and a foot formation; and a ratio of D₂:D₁ is in the range of 1:1 to 1:1.38; wherein: D₁ is a radial distance from the central longitudinal axis to a radially outermost extremity of the underlying base contour, corresponding to a junction between the base and a side wall of the self-standing container; and D₂ is a radial distance from the central longitudinal axis to a radially outermost extremity of the transition.
 2. The base of claim 1, wherein the ratio of D₂:D₁ is between 1:1 and 1:1.1.
 3. The base of claim 1, wherein the base has a volume to weight ratio of at least 19.4 ml per gram of PET, and wherein the wall thickness of a foot formation at a contact point is 0.18 mm.
 4. The base of claim 1, wherein a ratio of D₇:D₁ is approximately 1:1.63, wherein D₇ is the radial distance between the central longitudinal axis and a contact point of a foot formation.
 5. The base of claim 1, wherein a ratio of D₆:D₁ is approximately 1:1.76, wherein D₆ is the widest distance between two points on the transition which are radially equidistant from the central longitudinal axis; wherein a ratio of D₅:D₁ is approximately 1:2.62, wherein D₅ is the widest distance between two points on a foot formation which are radially equidistant from the central longitudinal axis and which do not form part of the transition; wherein a ratio of D₄:D₁ is approximately 1:1.36, wherein D₄ is the radial distance between the radially inner end of a foot formation, and radially outermost extremity of the transition; and wherein a ratio of D₃:D₁ is approximately 1:5.46, wherein D₃ is the radial distance between the central longitudinal axis and a radially inner end of a foot formation.
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. The base of claim 1, wherein a ratio of D₈:D₁ is approximately 1:1.17, wherein Dg is the axial distance between a planar surface on which a foot formation rests when standing and the radially outermost, axially uppermost extremity of the underlying base contour, corresponding to a junction between the base and a side wall of the self-standing container; wherein a ratio of D₉:D₁ is approximately 1:1.19, wherein D₉ is the axial distance between a planar surface on which a foot formation rests when standing and the radially outermost, axially uppermost extremity of the transition; wherein a ratio of D₁₀:D₁ is approximately 1:2.43, wherein D₁₀ is the axial distance between a planar surface on which a foot formation rests when standing and a line, parallel to that planar surface that passes through the two points on the transition which are the furthest apart from one another, and also radially equidistant from the central longitudinal axis; and wherein a ratio of D₁₁:D₁ is approximately 1:4.25, wherein D₁₁ is the axial distance between a planar surface on which a foot formation rests when standing and a line, parallel to that planar surface that passes through the two points on the foot formation which are the furthest apart from one another, and also radially equidistant from the central longitudinal axis, but do not form part of the transition.
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. The base of claim 1, wherein the underlying base contour is an oblate spheroid whose polar axis coincides with the central longitudinal axis of the base, and wherein the underlying base contour is substantially hemispherical.
 14. (canceled)
 15. The base of claim 1, wherein the foot formations are elongate ellipsoids and/or prolate spheroids, wherein the foot formations are ovoid, and wherein the widest part of the cross-section of each foot formation is offset inwardly toward an inner end of the foot formation.
 16. (canceled)
 17. (canceled)
 18. The base of claim 15, wherein the foot formations have respective longitudinal axes, which axes lie in planes extending radially from a central longitudinal axis of the base, wherein the axes of the foot formations extend outwardly in conical relation from the central axis of the base, wherein the axes of the foot formations extend outwardly and upwardly from the central axis of the base, and wherein the axes of the foot formations meet at the central axis of the base at a position axially below the base.
 19. (canceled)
 20. (canceled)
 21. (canceled)
 22. The base of claim 1, wherein the elliptical intersection is ovate, and wherein the elliptical intersection is of concave cross section.
 23. (canceled)
 24. The base of claim 1, wherein the base further comprises a stiffening formation disposed centrally between the feet.
 25. The base of claim 24, wherein the foot formations radiate from the stiffening formation.
 26. The base of claim 24, wherein the stiffening formation comprises concentrically arranged protrusions and depressions.
 27. The base of claim 26, wherein the concentrically arranged protrusions and depressions are joined via a sharply curving transition portion.
 28. The base of claim 1, wherein the foot formations are separated by valleys, wherein the valleys widen moving outwardly across the base, wherein each valley has an inner and an outer section and the walls of the valley diverge more sharply in the outer section than in the inner section, and wherein the walls of the valley diverge in both the inner and the outer sections of the valley.
 29. (canceled)
 30. (canceled)
 31. (canceled)
 32. The base of claim 1, wherein in plan view, each foot formation has an enlarged central region that tapers inwardly across an inner portion to an inner end of the foot formation, wherein the inner portions of the foot formations lie in segmented relation around the base, and wherein in plan view, each foot formation tapers from the enlarged central region outwardly across an outer portion to an outer end of the foot formation.
 33. (canceled)
 34. (canceled)
 35. A self-standing container having a base as defined in claim 1, wherein the container is stretch blow-moulded from a plastics preform, and wherein the base and a side wall are integrally moulded.
 36. (canceled)
 37. (canceled)
 38. The container of claim 35, wherein the foot formations of the base define respective contact points that together are spaced around a contact circle whose diameter (x) relates to a side wall diameter (Dy) of the container as: $\frac{Dy}{0.5\; x} = k$ where k is between 3.0 and 4.6, or between 3.1 and 3.5, or approximately 3.275.
 39. (canceled)
 40. (canceled)
 41. The container of claim 35, wherein the wall thickness of the base is in the range of 0.15 to 0.25 mm, or approximately 0.18 mm.
 42. (canceled)
 43. The container of claim 35, having an average burst pressure resistance to material usage ratio of greater than 3 MPa/kg, and a capacity to material usage ratio of greater than 40 litres/kg.
 44. (canceled) 